This multicenter, randomized, double-blind, placebo lead-in, parallel group study is designed to compare the safety and efficacy of a range of doses (50 to 400 mg) of SC-66110 to placebo. A dose of 100 mg of spironolactone administered daily in divided doses will be used as a reference. This study consists of a two week pretreatment period for washout of any current antihypertensive medication(s) and for completion of screening procedures. Washout is followed by a four-week single- blind placebo lead-in tratment, prior to randomization to an eight-week double-blind active and placebo treatment period.